Abstract

Objectives Kale（Brassica oleracea var. acephala）is a vegetable in the family Brassicaceae. Previous studies have suggested some beneficial effects of kale on health. To explore further evidence, we studied the effects of intake of kale on postprandial blood glucose and insulin levels in volunteers with relatively higher postprandial blood glucose levels in a randomized, double-blind, placebo-controlled crossover trial. Methods The trial was conducted with 19 Japanese subjects（10 males and 9 females aged from 20 to 64 years）with fasting glucose levels less than 126 mg╱dL and a 30︱min postprandial blood glucose level ranging 140-200 mg╱dL. Subjects consumed either placebo or 14 g of test food containing kale together with a carbohydrate-loading diet, and the levels of blood glucose and insulin were determined after 30-120 min. Results The postprandial blood glucose level at 60 min after the intake of test food（158.5±28.4 mg╱dL）was significantly lower than that of the placebo（171.2±25.9 mg╱dL; P＝0.035）. The maximum blood glucose level between 0 and 120 min following loading diet intake was also reduced significantly in the kale group（167.9±23.3 mg╱dL compared to 177.8 ±21.2 mg╱dL for the placebo group; P＝0.044）, and the area under the curve of blood glucose level was 286.1±43.8 mg・h╱dL in the kale group and 301.2±36.8 mg・h╱dL in the placebo group（P＝0.051）. No significant difference between the groups was observed with blood insulin level. There was no serious adverse event.Conclusions Our findings suggest that the consumption of test food containing kale reduces postprandial blood glucose level in subjects with relatively higher fasting blood glucose levels. The intake of kale as much as 14 g at a single dose was safe in humans.